Glow Plug Head And Corresponding Piezo-Electric Pressure Sensor

ABSTRACT

A glow plug includes a pressure sensor mounted within a tubular member ( 8 ) and held in the tubular member ( 8 ) by a bearing member. The bearing member is held in the tubular member ( 8 ) by plastic deformation ( 52 ) of the wall of the tubular member.

The present invention concerns a glow plug head and a piezo-electric pressure sensor adapted to be located in such a head.

It is known to integrate a pressure sensor in a glow plug in an internal combustion engine, in particular a Diesel engine. This sensor makes it possible to measure the internal pressure of the engine. The knowledge of this pressure enables the progression of the combustion in that engine to be better controlled. Better efficiency of that engine is thus attained and limitation is achieved not only of its fuel consumption but also of its polluting emissions.

A glow plug generally comprises a tubular body having on its outer surface a threaded portion enabling it to be fixed into a corresponding bore formed in a cylinder head. One portion of that body is located within the combustion chamber and the other portion outside it. The portion within the combustion chamber bears a finger within which is located a heater electrode. The latter is supplied by a core which passes through the tubular body of the glow plug. The portion outside the engine is also referred to as glow plug head. At that head, the core is connected to a source of electrical energy. It is also known to place the pressure sensor in that head.

For mounting such a pressure sensor, the Applicants have knowledge, not yet disclosed by them, of disposing that sensor in a housing provided for that purpose in the body of the glow plug. At the opposite end to the finger incorporating the heater electrode, an internal screw thread is formed and the pressure sensor is thus held in its housing by the fitting of a nut with an exterior screw thread. On its other face, the pressure sensor, of piezo-electric type, rests on a bearing member via an electrically insulating member and a spacer connects the finger of the glow plug to the bearing member. Thus, the pressure sensor is held by the nut and the spacer passes on, via the bearing member (and the electrically insulating member), the forces that are exerted on it by the pressure within the corresponding combustion chamber.

This assembly solution has first of all the drawback of requiring substantial machining particularly adjacent the head of the glow plug, and particularly of the body of that glow plug.

During the assembly of the glow plug and its pressure sensor, the various members are put in place and towards the end of the assembly the nut with external screw threading is put in place. It has then been noted that it is sometimes difficult to manage to obtain correct pre-stressing of the piezo-electric pressure sensor. This prestressing depends in particular on the machining tolerances and also on the roughness of the materials.

The present invention is therefore directed to providing an assembly of the sensor which makes it possible to alleviate these drawbacks and which in particular has a lower production cost and preferably giving a good ability to control the prestressing applied to the pressure sensor.

To that end, the invention provides a glow plug comprising a pressure sensor mounted within a tubular member and held in said tubular member by means of a bearing member.

According to the invention, the bearing member is held in the tubular member by plastic deformation of the wall of the tubular member.

In this way, it is possible to limit the machining operations for putting in place the pressure sensor compared with a solution in which the bearing member is screwed or else is held by a screwed member. This is because no screw threading is necessary here at the pressure sensor. Furthermore, by deforming the wall of the tubular member, it is possible to better control the stress exerted on the sensor. Lastly, during the plastic deformation carried out to hold the bearing member, no rotation is necessary and thus the parts within the glow plug are not driven rotationally.

In one embodiment of the invention, the bearing member is held by crimping.

For better holding of the bearing member, the latter advantageously has, at least over a portion of its periphery, a frusto-conical surface, the large diameter base of the frustum being oriented towards the pressure sensor.

An advantageous embodiment provides that the pressure sensor is a piezoelectric sensor comprising a piezoelectric member mounted between two contact members, and in that the piezoelectric member has an annular form having a flat on its periphery. This solution makes it possible to optimize the surface of the pressure sensor without having to modify the wall of the housing receiving the pressure sensor. In this embodiment, the piezoelectric member and the contact members are for example arranged substantially transversally in the tubular member; the contact members each have a connection tab at their periphery extending substantially longitudinally with respect to the tubular member, and the connection tabs are arranged in front of the flat of the piezoelectric member.

In a glow plug according to the invention, the tubular member may comprise an inner wall that is substantially circular cylindrical.

The tubular member receiving the pressure sensor may be a tubular body, generally termed glow plug body, enabling the glow plug to be fixed into an internal combustion engine cylinder head. It may however also be another part comprising a housing to receive the pressure sensor.

In the case in which the pressure sensor is mounted in the glow plug body and the latter is fixed in the cylinder head by screwing and comprises a gripping zone of hexagonal transverse section to facilitate its screwing and unscrewing, then the plastic deformation enabling the bearing member to be held in place is for example carried out adjacent to the gripping zone.

The present invention also concerns an internal combustion engine, in particular an engine of Diesel type, characterized in that it comprises at least one glow plug as described above.

Lastly, the invention also provides a method of mounting a pressure sensor in the head of a glow plug, in which the sensor is installed in a housing of adapted form then held by means of a bearing member.

According to the invention, the holding in place of the bearing member is achieved by plastic deformation of the wall of the housing receiving the sensor and the bearing member.

Details and advantages of the present invention will appear more clearly from the following description, made with reference to the accompanying drawings in which:

FIG. 1 shows an example of a glow plug earlier than the invention, in longitudinal cross-section.

FIG. 2 shows a side view of a glow plug according to the invention,

FIG. 3 shows a view from above of the glow plug of FIG. 2 at larger scale, and

FIG. 4 shows the piezo-electric sensor of the glow plug of FIGS. 2 and 3 in perspective and at large scale, with a corresponding bearing member.

FIG. 1 represents a longitudinal cross-section of a glow plug of a model prior to the invention (but not disclosed at the time of the first filing of the present patent application). This glow plug comprises a pressure sensor so as to be able to measure the pressure in an engine cylinder. This glow plug 2 is mounted in a conventional manner in an engine 4, of Diesel type, and more particularly in a cylinder head 6 of that engine. It comprises a body 8, a finger 10, a core 12 and a pressure sensor 14.

The body 8 is adapted to be fixed to the engine 4 by screwing To that end, the cylinder head 6 comprises a threaded bore passing through it and opening into a combustion chamber of said engine. Concerning the body 8, this has a screw thread 16 on its other surface corresponding to the bore formed in the cylinder head 6. When the glow plug is mounted in the engine 4, a portion of the body 8 extends towards the inside of the engine, that is to say towards the combustion chamber, whereas another portion extends towards the outside of the engine. The body 8 is a tubular body and is for example formed from steel.

In this embodiment (FIG. 1), the finger 10 is mounted within the tubular body 8, within which it has an interference fit, and projects into the combustion chamber. This finger 10 incorporates a heater electrode (not shown). The core 12 is adapted to supply that electrode with electrical energy and passes through the body 8 from the finger 10 as far as the opposite end of the body 8 from that at which the finger 10 projects. This core 12 is then connected, by means not shown, to a supply conductor.

The pressure sensor 14 is provided for measuring the pressure within the corresponding combustion chamber. In the embodiment of FIG. 1, this pressure sensor 14 comprises a piezo-electric member 18 disposed between two contact members 20 formed from an electrically conductive material. The sensor is then itself electrically isolated from the rest of the glow plug 2 by electrically insulating members 22.

In this embodiment, the pressure sensor 14 also comes to bear on the body 8 via a bearing member 24. The pressure sensor 14 is connected to the body 8 by its upper surface and bears against the finger 10 such that the pressure exerted on that finger compresses it against the body 8. To that end, the pressure sensor 14 bears on a spacer 38 which rests on the finger 10 and which is disposed in the body 8.

The compression of the pressure sensor 14 against the finger 10 (via the spacer 38 and the bearing member 24) as well as its connection to the body 8 is provided by a nut with external screw threading 36. This nut is not in contact with the core 12 but cooperates with an internal thread formed on the internal face of the side wall 46 of a housing 48 formed in the body 8 for receiving the pressure sensor 14.

The present invention provides for holding the pressure sensor 14 differently. FIG. 2 shows an external view of a glow plug according to the invention. This glow plug has, in longitudinal cross-section, for example a structure virtually the same as that represented in FIG. 1. Any other glow plug structure may of course also be envisaged here.

In the following portion of the description, the members of a glow plug according to the invention that are similar to those of the glow plug represented in FIG. 1 will be designated with the same reference numerals. Furthermore, it is considered that the glow plug has a particular orientation, and that its head comprising in particular the pressure sensor, is located towards the top whereas the finger of that glow plug, located within the engine, is considered as being towards the bottom.

The glow plug according to the invention also has a housing 48 similar to the housing 48 of FIG. 1. On the pressure sensor 14, a second bearing member 50 is put into place. The latter closes the upper open face of the housing 48. Whereas in the embodiment of FIG. 1 the closure of this housing 48 was provided by a nut with an external screw thread, which also served as bearing member for the piezo-electric sensor, the second bearing member 50 is here held by crimping. During the crimping operation, the side wall 46 of the housing 48 is plastically deformed so as to trap the second bearing member 50. In FIG. 2 indents 52 can be seen which result from this crimping.

As can be seen in FIG. 2, the body 8 of the glow plug has, at its head, a gripping zone 54 of hexagonal cross-section. The gripping zone 54 is used for the screwing and unscrewing of the glow plug into the cylinder head 6.

The head of the glow plug in FIG. 2 comprises the hexagonal gripping zone 54 in its lower portion. Above that gripping zone, the head of the glow plug has a circular cylindrical peripheral outer surface. The crimping is thus carried out at that circular cylindrical zone located above the gripping zone 54.

In the embodiment of the glow plug represented here, the piezo-electric pressure sensor is of generally annular form (a central hole is provided for the passage of the core 12) having a flat 56 at its periphery. The piezo-electric member 18, the contact members 20 as well as the second bearing member 50 reproduce this annular form having a flat 56.

The contact members 20, and the piezo-electric member 18, are transversely disposed with respect to the housing 48 which receives them. Each contact member 20 carries a connection tab 58 extending perpendicularly to the plane of the corresponding contact member 20. These connection tabs 58 thus extend longitudinally with respect to the housing 48 and extend substantially parallel to the core 12. As FIG. 3 shows, the fact of providing a flat 56 on the pressure sensor 14 makes it possible to house the pressure sensor 14 in the housing 48 without having to provide a cut-out or other in the side wall 46 of that housing in order to allow the passage of the connection tabs 58.

As can be noted in FIG. 4, the second bearing member 50 has a slightly frusto-conical form. The diameter of the lower face of that second bearing member 50, that is to say the face oriented towards the pressure sensor 14, is slightly greater than the diameter of the upper face of that said bearing member 50. During the crimping operation, the side wall 46 comes at least partially to espouse that frusto-conical form and this ensures the perfect retainment of the second bearing member 50 in the housing 48.

Compared with the retaining of the pressure sensor by a threaded plug (case of FIG. 1), the fact of fitting the sensor in its housing, and then covering it by a bearing member before deforming the side wall of the housing to trap that bearing member, and thus also the pressure sensor, is very desirable.

First of all, the machining costs for the corresponding glow plug are substantially reduced. More particularly, it is no longer necessary to produce an internal screw thread in the housing receiving the pressure sensor. The assembly is also facilitated, which makes it possible to have a reduced cost of assembly.

In a glow plug according to the invention, it is also easier, compared with glow plugs such as the one in FIG. 1, to control the prestressing applied to the pressure sensor when the housing in which that sensor is located is closed. When that housing is closed using a nut, the couple exerted on that nut is adjusted so as to obtain a stress on the pressure sensor. Depending on the manufacturing tolerances of the parts, and the roughnesses, it is then difficult to ensure a particular load on the sensor so held. The solution provided by the invention makes it possible to control that load much better.

Lastly during the fitting of the nut with external screw threading, the various components within the glow plug are driven rotationally. Of course, this drawback is not found with a glow plug according to the invention, as described above.

The present invention is not limited to the embodiment described above by way of non-limiting example. It also concerns all the variant embodiments accessible to the person skilled in the art.

Thus, the present invention may in particular apply to numerous glow plug structures incorporating a pressure sensor.

The method provided may apply when the pressure sensor is mounted in the body of the glow plug, but it may also apply when the sensor is mounted in a housing in another part. 

1. A glow plug (2) comprising a pressure sensor (14) mounted within a tubular member (8) and held in said tubular member (8) by means of a bearing member (50), characterized in that the bearing member (50) is held in the tubular member (8) by plastic deformation of the wall (46) of the tubular member.
 2. A glow plug according to claim 1, characterized in that the bearing member (50) is held in place by crimping.
 3. A glow plug according to claim 1, characterized in that the bearing member (50) has, at least over a portion of its periphery, a frusto-conical surface, the large diameter base of the frustum being oriented towards the pressure sensor (14).
 4. A glow plug according to claim 1, characterized in that the pressure sensor (14) is a piezoelectric sensor comprising a piezoelectric member (18) mounted between two contact members (20), and in that the piezoelectric member (18) has an annular form having a flat (56) on its periphery.
 5. A glow plug according to claim 4, characterized in that the piezoelectric member (18) and the contact members (20) are arranged substantially transversally in the tubular member (8), in that the contact members (20) each have a connection tab (58) at their periphery extending substantially longitudinally with respect to the tubular member (8), and in that the connection tabs (58) are arranged in front of the flat (56) of the piezoelectric member (18).
 6. A glow plug according to claim 1, characterized in that the tubular member (8) comprises a substantially circular cylindrical inner wall.
 7. A glow plug according to claim 1, characterized in that the tubular member (8) receiving the pressure sensor (14) is a tubular body (8) enabling the glow plug (2) to be fixed in the cylinder head (6) of the internal combustion engine.
 8. A glow plug according to claim 7, characterized in that the tubular body (8) is fixed in the cylinder head (6) by screwing and comprises a gripping zone (54) of hexagonal transverse section to facilitate its screwing and unscrewing, and in that the plastic deformation enabling the bearing member (50) to be held in place is carried out adjacent to the gripping zone (54).
 9. An internal combustion engine, in particular of the Diesel engine type, characterized in that it comprises at least one glow plug (2) according to claim
 1. 10. A method of mounting a pressure sensor (14) in the head of a glow plug (2), in which the sensor is installed in a housing (48) of adapted form then held by means of a bearing member (50), characterized in that the holding in place of the bearing member (50) is achieved by plastic deformation of the wall (46) of the housing (48) receiving the sensor and the bearing member (50).
 11. A glow plug according to claim 2, characterized in that the bearing member (50) has, at least over a portion of its periphery, a frusto-conical surface, the large diameter base of the frustum being oriented towards the pressure sensor (14).
 12. A glow plug according to claim 2, characterized in that the pressure sensor (14) is a piezoelectric sensor comprising a piezoelectric member (18) mounted between two contact members (20), and in that the piezoelectric member (18) has an annular form having a flat (56) on its periphery.
 13. A glow plug according to claim 3, characterized in that the pressure sensor (14) is a piezoelectric sensor comprising a piezoelectric member (18) mounted between two contact members (20), and in that the piezoelectric member (18) has an annular form having a flat (56) on its periphery. 